A polyolefin composition and a thermoplastic elastomer based upon a semi-crystalline polyolefin are described which have improved adhesion to polar polymers including textile fibers and metals including wires. A combination of a low flexural modulus (low crystallinity) polypropylene and a maleic anhydride functionalized polypropylene were found to exhibit excellent adhesion to textile fibers. Incorporation of these two components into a TPE (thermoplastic elastomer) imparts excellent adhesion of the TPE to textile fibers.
Polyolefins and thermoplastic elastomers rich in polyolefins have traditionally had poor adhesion to textile fibers. Experiments with thermoplastic vulcanizates (TPV), a subset of thermoplastic elastomers (TPE), using formulations similar to those of U.S. Pat. Nos. 4,130,534 and 4,130,535 resulted in peel strengths of only 0.5 to 1.0 pounds per linear inch (pli) between the TPV and textile fibers after melt processing the TPV to the textile fibers. The industrial hose and belting markets generally require a peel strength of at least 8 to 12 pli for candidate matrix materials for fiber reinforced hoses and belting. While polyolefins and TPVs from polyolefins have benefits over plasticized polyvinyl chloride resin (in terms of chemical resistance and physical properties after aging) and over crosslinked rubbers (in terms of processability and physical properties after aging) their use with textile fibers has been limited due to low adhesion values (low peel strengths).
U.S. Pat. No. 4,957,968 teaches adhesive thermoplastic elastomer blends comprising a) at least a polyolefin modified by a chemically reactive functional group, b) at least one other polymer, and c) at least one olefinic elastomer.
Typically, when a polymer and a fiber exhibit poor adhesion toward each other, the problem is attributed to poor wetting of the fiber with the polymer or a lack of good interactions between the fiber surface and the polymer. If processing aids are not effective in solving the wetting problem, then different fibers or a different polymer is chosen or a sizing, more interactive with the specific polymer, is applied to the fiber.
A combination of two polymers was found that improves the interaction of polyolefins and/or thermoplastic vulcanizates (TPV) with more polar polymers and metals, especially various textile fibers and metal wires. More polar polymers are defined as those polymers more polar than polyolefins due to the inclusion of heteroatoms such as oxygen or nitrogen in the repeating groups. The first polymer is a low crystallinity polyolefin with a low flexural modulus (tangent) such as from about 5,000 to about 20,000 psi (34.5 to 138 MPa). It is hypothesized that the low flexural modulus helps reduce stress at the bond line between the polyolefin and the fiber and/or polar polymer. The first polymer may be characterized as a polyolefin polymer or copolymer with only 10 to 30 percent crystallinity. As described later the first polymer with low crystallinity and a low modulus may be a blend (reactor blend, physical blend, etc.) of a very low crystallinity polymer with a conventional semi-crystalline polyolefin. The second polymer is a functionalized polyolefin (e.g. semicrystalline polyolefin) with from about 0.5 to about 3.5 mole percent of functional repeating units. Preferred functional groups are carboxylic acid groups and/or anhydride from a di or poly carboxylic acid. For the purposes of this application the polyolefin can be derived from polymerizing monoolefins or from polymerizing diolefins and then hydrogenating them to obtain similar microstructures to polyolefins. These polyolefins from diolefins can be block copolymers with other monomers such as stryene.
In some embodiments, the functionalized polyolefin and the polyolefin with the low flexural modulus and low crystallinity are the only required components of a hot-melt composition with excellent adhesion to polar polymers and textile fibers.
In another embodiment, a crosslinked rubber is present so that the rubbery properties of a thermoplastic vulcanizate are present.
In yet another thermoplastic vulcanizate embodiment, both a conventional high modulus polyolefin and rubber are present. The high modulus polyolefin can increase the stiffness and/or increase the softening temperature of the composition for uses requiring stiffness or having a higher use temperature requiring a higher softening temperature for the TPV.
Any of the above compositions can be used to adhere to polar polymers, metal, high tensile strength fibers and/or sheets. The excellent adhesion attributed to the combination of functionalized polyolefin and low crystallinity and low flexural modulus polyolefin is well utilized in melt processing a thermoplastic vulcanizate around a fiber or metal (e.g. wire) reinforced assembly.
Hydrosilylation crosslinking is a particularly advantageous type of crosslinking for the rubber phase as it has minimal side reactions with the functionalized polyolefin allowing the functionalized polyolefin to be blended with the other components before crosslinking the rubber phase.